The present invention relates to speed ratio control of an automatic transmission, and more particularly, to a speed ratio control device wherein the effectiveness of engine braking is enhanced when there is a change-over from an automatic shift to mode to a manual shift mode.
In one type of automatic transmission for vehicles, a selection can be made between an automatic shift mode and a manual shift mode. JP-A-H9-196156 and JP-A-H9-264416, which were published by the Japanese Patent Office in 1997, disclose a speed change device which selects a gear position such that the fluctuation of an input rotation speed becomes small before and after a change-over from an automatic shift mode to a manual shift mode.
In general, when a driver changes over from an automatic shift mode to a manual shift mode, he often expects a downshift for acceleration immediately after the change-over or a downshift to enhance the effectiveness of engine braking.
However, in the aforesaid prior art device, there is not always a downshift immediately after the change-over, and it is not possible to appropriately satisfy this demand.
It is therefore an object of this invention to ensure a downshift for a subsequent acceleration or the enhancement of engine braking by selecting a gear position at which a transmission input rotation speed will definitely be above a predetermined value when there is a change-over from the automatic shift mode to the manual shift mode.
In order to achieve above object, the present invention provides a speed ratio control device for use with a vehicle provided with an automatic transmission. The device comprises an actuator which varies a speed ratio of the transmission, and a microprocessor for controlling the actuator and programmed to vary the speed ratio automatically according to a running state when an automatic shift mode is selected, vary the speed ratio based on a manual operation when a manual shift mode is selected, and set the speed ratio immediately after a change-over is made from the automatic shift mode to the manual shift mode, to a speed ratio which increases a transmission input rotation speed after the change-over more than a predetermined rotation speed compared to the transmission input rotation speed before the change-over.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.